In recent years, prefilled syringes including a syringe barrel preliminarily filled with a liquid drug are increasingly used, because they are easy to handle and prevent use of a wrong liquid drug. Since rubber members (e.g., a gasket and a nozzle cap) of such a prefilled syringe are kept in direct contact with the liquid drug until use, the gasket and the nozzle cap are generally made of a butyl rubber which is excellent in chemical resistance, gas barrier property, water vapor barrier property and anti-aging property.
However, some biological drugs are liable to be influenced by interaction with the rubber members and substances released from the rubber members. For improvement of the slidability of the gasket and prevention of the sticking of the nozzle cap, an inner wall of the syringe barrel and surfaces of the gasket and the nozzle cap made of the butyl rubber are often coated with a lubricant such as a silicone oil or a curable silicone. The silicon coating is liable to be separated from the barrel inner wall and the rubber members to significantly adversely influence some types of drugs.
To cope with this problem, rubber products laminated with a fluororesin film or the like to obviate the need for the silicone are developed for use in a glass syringe or a prefilled resin syringe.
A PTFE (polytetrafluoroethylene) film having an excellent chemical resistance and a minimum friction coefficient is suitable as the fluororesin film for the lamination of the gasket. Where the use of the silicone lubricant is permitted, an ETFE (ethylene tetrafluoroethylene) film may be used for the lamination. The PTFE film is typically produced by a skiving method, a casting method or the like.
A gasket having a fluororesin film provided on a liquid contact surface thereof and a slidable seal portion thereof to be kept in contact with the inner wall of the syringe barrel has problems associated with gas tightness and sliding resistance. Particularly, the film produced by the skiving method is liable to cause the problem associated with the gas tightness with respect to the inner wall of the syringe barrel because of its greater surface roughness.
Factors relevant to deterioration of the gas tightness are the smoothness (surface roughness) of the film used for the lamination, and variations in the inner diameter of the syringe barrel which influence the compression percentage of the gasket with respect to the inner diameter of the syringe barrel. The resin syringe barrel has a highly accurate inner diameter with a tolerance of ±0.1 mm. On the other hand, a material tube for the glass syringe barrel has greater variations in inner diameter, and even a glass syringe barrel having a volume of not greater than 5 mL has a relatively great inner diameter tolerance of ±0.15 mm.
Even if a PTFE film having a surface roughness Ra of not greater than 0.05 μm is used for the lamination, liquid leakage often occurs. This is because, even if the PTFE film is lamination-molded at a molding temperature of 170° C. (which is lower than the melting point (230° C.) of the PTFE), minute undulations of a mold surface are transferred to the surface of the lamination film to thereby influence the sealability.
To solve the problems associated with the gas tightness and the sliding resistance, there are proposed a gasket having a cylindrical drum shape (e.g., Patent Document 1), and a gasket having a plurality of annular ribs provided on a circumferential surface of a cylindrical gasket body (see, for example, Patent Document 2 and FIG. 3(e) in Patent Document 3).